Investigators are speaking with three paramedics involved in the fatal winching accident in which a man plunged to his death from a rescue helicopter.

The 68-year-old man was at the door of the helicopter hovering around 30 metres off the ground when something went wrong and he fell to his death.

The man had been hiking through a heavily bushed part of Victoria northeast of Melbourne when he broke his ankle on Saturday morning.

Two former helicopter pilots and two aircraft engineers from the Australian Transport Safety Bureau (ATSB) began interviewing the paramedics involved on Sunday as part of an investigation into the tragedy.

"We'll be examining the helicopter itself, the winching equipment, interviewing the crew and it may be necessary to take some parts of helicopter," ATSB manager Greg Madden said.

The ATSB is one of three bodies investigating the accident, along with Ambulance Victoria and WorkSafe Victoria.

Ambulance Employees Australia general secretary Steve McGhie said the crew had been left shaken by the fatal fall.

"I've spoken to one of the air paramedics and he's understandably upset," McGhie said.

"It's a terrible accident and someone has lost their life."

He said he believed the size of the patient, the nature of his injury and the terrain necessitated the air ambulance.

The paramedics were drug tested late Saturday as part of standard procedure in such investigations, McGhie said.

Ambulance Victoria has suspended all winching operations until it's finished its own investigation.

"Once we understand what occurred and whether there's equipment involved or not that suspension may be lifted," Ambulance Victoria chief executive Greg Sassella said on Saturday.

Victoria Police have yet to release the name of the Riverwood man who died in the fall, but will prepare a report for the coroner.